1. Field of the Invention
The invention relates to apparatus for mounting a wheel on a vehicle and more particularly to mounting apparatus providing a predetermined, uniform clamping force around an annular zone of contact between the mounting apparatus and the vehicle wheel thereby securing the wheel to the wheel mounting flange upon which it is mounted.
2. Description of the Prior Art
A conventional vehicle wheel is mounted by means of a plurality of lug nuts threaded onto stud bolts extending outwardly from a wheel mounting flange, such as a flanged hub or an axle flange, through bolt holes in the spider of the wheel. The wheel mounting flange in a conventional wheel assembly includes an outwardly-extending end that receives and engages a central pilot hole in the wheel spider. The lug nuts generally have coneshaped seats that engage correspondingly-sloped bosses surrounding the bolt holes in the wheel spider.
In a conventional wheel assembly, the required axial clamping force to secure the wheel to the wheel mounting flange is obtained by tightening the lug nuts to a specified torque level. Thus, the clamping force is directly dependent upon the friction between the lug nut threads and the stud bolt threads and, more significantly, between the lug nut seats and the wheel spider bosses around each bolt hole. The coefficient of friction between these mating surfaces changes dramatically from the first time the wheel is mounted. Such changes primarily result from wear and material deformation each time the lug nuts are removed and re-installed during tire changing, tire rotation and vehicle inspections.
Because of the above-described changes in friction, the torque needed to adequately tighten the lug nuts varies drastically. Thus if the friction on a particular lug nut increases, that nut may be tightened to the specified torque level but the clamping force provided by it may be too low. Conversely, if the friction on another lug nut on the same wheel decreases, that nut may also be tightened to the proper torque level but provide a clamping force significantly higher than that provided by the other nuts on the same wheel. Therefore, lug nut torque has proven to be a rather poor indicator of the axial clamping force securing the wheel to the wheel mounting flange. As a result, wide variances in clamping force from lug nut to lug nut may be present on the same wheel. Such non-uniform and unknown clamping forces frequently cause warping, twisting and distortion of the wheel spider, the brake rotor or drum, and other vehicle components, all of which seriously decrease the performance and life of the affected component. Thus a wheel mounting means is needed that is capable of providing a repeatable, predetermined and uniform axial clamping force on a vehicle wheel.
Single fastener wheel assemblies using washer-type discs are known in the prior art of which U.S. Pat. Nos. 1,681,503; 1,691,488; 1,813,431; and 1,816,643 are exemplary. The devices disclosed in the prior art, however, neither accomplish the objects of the present invention nor incorporate its novel features.